The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs.
For example, there is considerable interest in providing consumer and/or portable electronic devices (e.g., smart phones, electronic tablets, wearable devices, and so on) with biometric sensors (e.g., optical sensors for fingerprint recognition) inside limited device housing. Surface space is often a particularly limited resource in electronic devices. A need exists for biometric sensors to stack with other components (e.g., display panels) inside device housing to avoid assigning valuable surface space exclusively to biometric sensors that may only be used briefly during a user identification step. By stacking biometric sensors, a biometric object (e.g., a user's finger) outside the electronic device is further distanced away from the sensors. Interferences from stray light and ambient light may grow stronger, resulting in poorer sensitivity of the biometric sensors. For example, fingerprint images acquired by an optical biometric sensor may become blurred due to degradation of signal-to-noise ratio (SNR) of received light under the interferences. Therefore, although conventional means of integrating biometric sensors inside electronic device housing have been generally adequate for their intended purposes, they are not satisfactory in all respects.